MCSCF is not a “black box” procedure like SCF! For simple cases, for example a simple
CASSCF with no CLOSED orbitals, this program will converge in two or three
iterations. For more complicated cases, you may have more trouble. In that case, consider
the following:

Always start from neighbouring geometry orbitals when available (this is the
default).

The convergence algorithm is more stable when there are no CLOSED
orbitals, i.e., orbitals doubly occupied in all configurations, but
fully optimized. Thus a reasonable approach is to make an initial
calculation with CLOSED replaced by FROZEN (all doubly occ. frozen).

If still no success, you can switch off the coupling between CI
coefficients and orbital rotations for a few iterations, e.g.:

You can often get a clue about where the program starts to diverge if you include:

IPRINT,MICRO;

in the data. Also consider the general remarks at the beginning of this chapter. For the
details of the algorithms used, see J. Chem. Phys 82, 5053 (1985); Chem. Phys. Letters 115,
259 (1985); Advan. Chem. Phys. 59, 1 (1987);